You could get paid for your work. Someone hires you and you make software. They get software, you get the software and you got paid. This program was created to better the world. A seed of knowledge has been planted. You share this knowledge. You use the knowledge. Someone else might use it. You talk about it, exchange ideas, and work on it. You create something better. Someone hires you. You both know the conditions. You, as a computer hacker, build their computer systems, and everybody are entitled to the knowledge obtaint in the progress. You could gather your best fellow computer hackers and do the work together.

Nothing in the GNU license requires you to disclose your clients.
Everything you write is your work. You own it. So when a guy sells a program you made half of and he made the other half, you are legally entitled to half the money. You just have to prove that you actually made half the work. Unfortunately the Free Software Foundation (FSF) only have the funds to enforce its own work, and not individual works.
I am not a layer, so I do not know precisely how the text read. But I know you as a individual have som form of legal protection.

Companies might want to initiate their own project. Because they have greater needs, they will need a lot of people working on their software. The company is in a position to sketch the lines, and use their influence to guide the progress. What they get for this is software specificly tailored to their needs, for no price at all but the time they invest, and everybody gets acces the knowledge obtained in the progress. If a company had thousands if coders working on the project and they (the company and project leader) provided the correct guidiance, the system would be far better for them than any propitary system could ever be. Because they made it themselves.

The thought behind free software basicly asks you if you want to control your software or you want other to control your software. And the answer of course is, you want to control your software because no one knows better what you need than you .